1. Field of the Invention
The present invention relates generally to the field of motorcycle engines and more specifically to an improved cranking system for chain or belt-driven V-Twin motorcycle engines in which by employing a direct drive cranking motor configuration, maximum cranking power is achieved for a conventional motorcycle battery.
2. Background Art
Conventional chain or belt-drive V-Twin motorcycle engines employ a chain or belt to transmit power from the engine crankshaft to the transmission and normally employ a cranking motor which is remotely coupled to the engine crankshaft by the belt or chain using an axially movable shaft controlled by a cranking motor clutch and a selected gear reduction from the cranking motor to the crankshaft. Because of typical volume constraints on even the larger motorcycles which employ V-Twin engines, the size of the battery is severely limited. A typical battery for this purpose is a 22 Amp/hour 12 volt battery capable of about 1.6 kW to 1.8 KW maximum energy output. This maximum output of the battery is achieved only at the ideal operating point during cranking which is at a cranking current of about 200 Amps at about 8 volts. Cranking motors are also designed to deliver peak power at 8 volts. The battery power output becomes less than ideal at higher cranking currents because of a further rapid drop in output voltage as does that of the cranking motor. With larger V-Twin engines, it becomes even more critical to operate the battery and cranking motor at their respective maximum efficiencies in order to reliably start the engine. However, because of gear ratios dictated by the nature of the cranking motor, its size and position and the use of a chain or belt drive to link the cranking motor to the crankshaft, the battery and cranking motor are instead operated at very low efficiencies. As a result, the starting cranking power is marginal at best and the current drain on the battery quickly dissipates the available starting energy; a very unfavorable combination. By way of example, a typical V-Twin chain drive motorcycle engine employs a remote cranking motor having a 4.4:1 internal gear reduction which was originally designed for a 10 tooth pinion gear and a 140 to 150 tooth ring gear. This starter should result in an overall gear reduction from the armature of the electric motor in the cranking motor to the crankshaft of about 64 which is typical of automotive applications and presents the near ideal situation. However in a V-Twin chain drive motorcycle, the actual gear ratio is between 21 and 40, resulting in a gear ratio-induced mismatch of between 2 and 3 to 1. Consequently, there is a complete mismatch as well between the battery characteristics, the cranking motor characteristics and the engine cranking requirements. The battery and cranking motor both operate at very low efficiency, resulting in only a small fraction (25%) of the maximum power capability that could be delivered if each of the battery and cranking were operating at their maximum power points. With aftermarket modifications to increase engine output, including using bigger V-Twin engine displacement and the like, this problem has been exacerbated to the point of unreliable starting and the need for frequent cranking motor and cranking motor clutch replacement. Moreover, batteries also require frequent replacement due to repeated extremely high current discharges.
Thus, it would be highly advantageous if there were a convenient way to operate a cranking motor in a V-Twin chain or belt-driven motorcycle engine so that a conventional small size motorcycle battery and cranking motor could more efficiently apply battery cranking power to the crankshaft to more reliably start such an engine. It would also be highly beneficial to find a way to convert the cranking configuration of such engines to achieve that same result.